1. Field of the Invention
The present disclosure relates to an image forming device and an image forming method which are adapted to discharge a recording liquid to a recording sheet to form an image on the recording sheet.
2. Description of the Related Art
Conventionally, in order to speed up image formation processing in an image forming device, such as an ink-jet printing device, a bidirectional printing in which ink is discharged in both a forward path and a backward path parallel to a main scanning direction (which is perpendicular to a transporting direction of a sheet) has been used. However, when the bidirectional printing is performed in such an image forming device, there is a problem that color banding (or color irregularity) in a sub-scanning direction (which is perpendicular to the main scanning direction) may arise. Various image forming devices have been proposed in order to solve this problem.
Japanese Laid-Open Patent Publication No. 2004-106392 discloses an ink-jet printer in which color nozzles of a printing head are arranged in the nozzle row direction, and bidirectional color deviation is reduced by unifying the impact sequence of the nozzles to discharge color ink in the forward and backward directions. The speed of black monochrome printing is increased by using black nozzles arranged in the head independently of the color nozzles.
Japanese Laid-Open Patent Publication No. 2001-171151 discloses an ink-jet printer in which the impact sequence of color-nozzle multiple heads in the bidirectional printing is unified by selectively using one of the multiple heads for the forward path in the main scanning direction and the multiple heads for the backward path in the main scanning direction.
Japanese Laid-Open Patent Publication No. 2005-305959 discloses an ink-jet printing head in which two groups of color nozzles are arranged symmetrically and arrayed side by side with each other in the sub-scanning direction in order to unify the impact sequence of the nozzles and increase the speed of image formation.
However, each of the ink-jet printer of Japanese Laid-Open Patent Publication No. 2004-106392 and the ink-jet printer of Japanese Laid-Open Patent Publication No. 2001-171151 requires a complicated printing head structure or multiple printing heads. As for the ink-jet printing head of Japanese Laid-Open Patent Publication No. 2005-305959, it is difficult to unify the impact sequence of the color nozzles completely for both the forward path and the backward path in the main scanning direction, and color banding may arise.